The present invention relates to methods of manufacturing backrest structures of seats for vehicles and the backrest structures produced by this method.
More specifically, the invention relates to a method of manufacturing a backrest structure of a seat for a vehicle, this structure comprising:
a tubular-shaped, rigid, bottom horizontal crosspiece delimiting a certain interior volume and comprising a bottom part and a top part,
a tubular-shaped, rigid, top horizontal crosspiece delimiting a certain interior volume and comprising a bottom part and a top part,
and at least first and second rigid, substantially vertical uprights, each of which extends between bottom and top ends joined respectively to the bottom and top crosspieces,
said method comprising at least one step in which the bottom and top crosspieces are shaped by hydroforming.
A method of this type is described in document FR-A2 753 935, for example, whereby one of the lateral uprights of the structure is made from a single piece with two crosspieces from a same tubular section, this unit then being welded onto the other lateral upright.
This method is quite satisfactory but has a disadvantage in that said other lateral upright can only be joined to the bottom and top crosspieces by welding, which is relatively expensive.
In addition, the weld seams are always critical points of the backrest structure and have to be controlled very carefully, thereby complicating the process of manufacturing the backrest structure.
These disadvantages are major under all circumstances but become critical if the backrest structure is made from aluminium or an aluminium-based alloy insofar as welding these materials is a particularly delicate operation.
The objective of the present invention is to overcome these drawbacks.
To this end, the invention proposes a method of the type outlined above, which is characterized in that when hydroforming the bottom crosspiece, whilst the interior volume of this bottom crosspiece is being filled with pressurized liquid, at least first and second pairs of orifices are punched into said bottom crosspiece, the first pair of orifices in the bottom crosspiece comprising two reciprocally matching orifices arranged respectively in the top part and in the bottom part of the bottom crosspiece and having sections matching the bottom end of the first upright, and the second pair of orifices of the bottom crosspiece comprising two reciprocally matching orifices arranged respectively in the top part and in the bottom part of the bottom crosspiece and having sections matching the bottom end of the second upright,
in that when hydroforming the top crosspiece, as the interior volume of this top crosspiece is being filled with pressurized liquid, at least first and second pairs of orifices are punched into said top crosspiece, the first pair of orifices of the top crosspiece being two reciprocally matching orifices arranged respectively in the bottom part and in the top part of the top crosspiece and having sections matching the top end of the first upright and the second pair of orifices of the top crosspiece being two reciprocally matching orifices arranged respectively in the bottom part and in the top part of the top crosspiece and having sections matching the top end of the second upright, and in that the hydroforming step is followed by an assembly step, in which:
the bottom ends of the first and second uprights are engaged without any clearance respectively in the first and second pairs of orifices of the bottom crosspiece,
the top ends of the first and second uprights are engaged without any clearance respectively in the first and second pairs of orifices of the top crosspiece,
and the uprights are definitively joined to the crosspieces in order to prevent the uprights from slipping out, mechanical strength essentially being imparted to the backrest structure by the location of the uprights in the crosspieces without any clearance.
As a result of these features, the mechanical strength of the backrest structure is essentially obtained by a location fit which is very easy to implement and control.
Optionally, weld seams or spots may be applied to join the uprights onto the crosspieces definitively but these welds have virtually no role to play with regard to the mechanical strength of the backrest and are therefore not critical points of the structure.
In any event, the welding will be on a much lesser scale than required by the methods the prior art.
Furthermore, the method proposed by the invention will easily absorb the manufacturing tolerances on the length of the vertical uprights of the backrest structure.
Furthermore, the same hydroforming equipment may be used to make backrest structures of the same external shape but incorporating material of differing thicknesses, which will reduce the cost of manufacturing backrest structures since a same backrest structure (for example, a backrest for xe2x80x9c3 seaterxe2x80x9d vehicles and for xe2x80x9c2 seaterxe2x80x9d vehicles in which the boot is not totally separated from the area reserved for the rear passengers).
Finally, the operation whereby orifices are punched into the crosspieces is a commonplace operation in the hydroforming process, which will be made no more complex or expensive as a result.
Optionally, the backrest structure may have at least two seats side by side, this structure having a third rigid, substantially vertical upright which extends between bottom and top ends joined respectively to the is bottom and top crosspieces, the method comprising the following additional steps:
when hydroforming the bottom crosspiece, at least a third pair of orifices is punched into a top part of said bottom crosspiece, the third pair of orifices in the bottom crosspiece comprising two reciprocally matching orifices arranged respectively in the top part and in the bottom part of the bottom crosspiece and having sections matching the bottom end of the third upright,
when hydroforming the top crosspiece, at least a third pair of orifices is punched into a bottom part of said top crosspiece, the third pair of orifices in the top crosspiece comprising two reciprocally matching orifices arranged respectively in the bottom part and in the top part of the top crosspiece and having sections matching the top end of the third upright,
the bottom and top ends of the third upright are engaged without clearance respectively in the third pairs of orifices of the bottom and top crosspieces,
and the third upright is definitively joined to the crosspieces in order to prevent the third upright from slipping out, mechanical strength essentially being imparted to the backrest structure by the location fit of the first, second and third uprights in the crosspieces without any clearance.
The invention also relates to a backrest structure produced by the method described above, this structure optionally comprising one and/or other of the following features:
the vertical uprights are definitively joined to the crosspieces by welding;
the vertical uprights are definitively joined to the crosspieces by clamping;
the backrest structure is made from steel;
the backrest structure is made from a material selected from aluminium and aluminium-based alloys;
the bottom and top crosspieces have gutters designed to attach a cap covering the backrest, these gutters being cast with said crosspieces from the same material;
the bottom crosspiece forms flanges designed for pivotally mounting the backrest on the vehicle, these flanges being cast with said bottom crosspiece from the same material;
the top crosspiece also has at least one additional punched orifice into which an element selected from the following is fixed:
a pin for a headrest,
a riveted fixing insert,
a backrest bolt,
a plate for a backrest bolt,
a mounting for a safety belt reel,
an outlet for a safety belt strap;
the backrest structure has at least one place for a user and the bottom crosspiece has a portion that is flattened on a substantially vertical plane on a level with this seat.